Compound interest means that after each interest period, the interest and principal generated are included in the interest of the next period in the form of cost. Compound interest is to generate interest with interest, which is also commonly known as rolling interest.

Not all funds are calculated by compound interest, but only the fixed investment of the fund. There is no compound interest in the fixed investment of the fund itself, but when the fixed investment fund distributes the income and chooses the way of dividend reinvestment, there will be compound interest. Fixed investment is the abbreviation of fixed-term investment fund, which refers to a way to invest a fixed amount in a designated open-end fund at a fixed time, similar to the bank's zero deposit and withdrawal method.

When calculating the compound interest of fixed investment, the principal amount of each period is different, which is mainly used to calculate the final principal and interest value of multiple equal investments and the value of multiple equal returns. Compound interest includes intermittent compound interest and continuous compound interest. The method of calculating compound interest by year, half year, quarter and month is intermittent compound interest, and the method of calculating compound interest by moment is continuous compound interest.